Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

120
FXUS63 KLOT 151951
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
251 PM CDT Mon Jun 15 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected on Tuesday. A
  storm may become severe east of I-39 after 12 PM.

- Additional thunderstorms are expected in the region Wednesday
  into Wednesday evening with a level 3 Risk for severe
  weather. All hazards are possible including large hail,
  damaging winds and tornadoes.

- Torrential rainfall and localized flash flooding are possible
  Wednesday.

- Possible high waves and dangerous swimming conditions may
  occur at Indiana Lake Michigan beaches Thursday.

&&

.DISCUSSION...
Issued at 251 PM CDT Mon Jun 15 2026

Conditions are comfortably mild on this Monday afternoon with
temperatures in the lower and middle 70s and a mix of fair
weather cumulus and broken cirrus filtering our largely blue
sky. A dry regional airmass in place will keep conditions quiet
through the night while the high level cloud cover continues to
expand ahead of our next precip chances. Morning lows are
forecast in the 50s with slightly warmer temperatures generally
expected in and around the city.

Water vapor imagery depicts the early stages of a shortwave
disturbance spinning up over the northern Plains on the nose of
the upper jet max. This wave will sharpen up through the night
and drive a surface low across the upper Midwest tomorrow. The
associated cold front is progged to pass through during the
afternoon. Before it does, a line of showers and storms is
expected to develop along the front over MN tonight and outrun
it before moving across the CWA tomorrow morning. Little forcing,
dry air, and limited low level instability out ahead of the
front look to limit thunder coverage through most of the
morning. A number of camps do have the line intensifying to some
degree across our eastern CWA late morning and into the
afternoon as instability builds. As the actual front moves
across in the afternoon, the added forcing for ascent both along
the front and on the nose of a modest low level jet, an increase
in shear, and a possible tongue of higher dewpoints ahead of
the boundary will make it possible for a stronger storm or two
to fire up in the afternoon. Guidance is in favor of storms
building south along the front later in the day, but a big
majority of camps hold out until later in the afternoon when the
front is just off to our east. The NAM and NAM Nest are most
bullish on this afternoon potential owing to a sliver of lower
60s dewpoints in our east ahead of the front (in typical NAM
fashion) while most others insist the dry air will be too
limiting. SPC`s Level 1 of 5 Marginal Risk east of I-39 seems
very appropriate in this conditional setup.

An upper jet max will push onshore the British Colombia coast
tonight and evolve into a vigorous shortwave as it ejects
southeast out of the High Plains late Tuesday into Wednesday. At
the surface, a deepening center of low pressure will cut across
the Midwest on Wednesday. Coupled with a speedy southerly warm
conveyor featuring 60+ kt at 850 mb and a strong westerly 500mb
jet max nosing into the region, the kinematic environment looks
to be highly conducive of organized severe convection during the
latter part of Monday. The limiting factor in this case may be
the amount of available instability and, as per usual with such
a dynamic system, there remain considerable model uncertainties.

Guidance is in favor of a push of showers and thunderstorms
during the morning as the more impressive kinematic features
work into the region. Some camps even resolve a messy MCV
spinning up in the high shear environment, but limited elevated
instability should hinder much of a severe threat during the
morning. However, we will find ourselves in a favorable
environment for gravity wave associated convection on the
eastern edge of this strengthening jet max which could provide
a sneaky severe wind threat with this morning push despite the
lack of instability. Today`s 06 and 12Z runs of the RRFS even
hint at this by resolving evenly spaced thunder cores with
strong wind gusts during the morning, a tell tale sign of GWAC.

The better severe potential exists during the afternoon and
evening as the storm`s cold front passes through. The big
question for the PM severe potential is how far north the
effective warm front lifts amid the morning convection prior to
the cold frontal passage. The greatest severe threat will be
found near and south of this front where just about all boundary
layer instability will be confined. The anomalously strong low-
mid level wind field will result in eye-catchingly long,
looping hodographs that will be especially concerning for
surface-based storms. All severe hazards are on the table for
areas along and south of the front including damaging to
destructive wind gusts and tornadoes, some possibly strong.
There is uncertainty in how much elevated instability will be
found north of the front for an elevated wind or hail threat,
but shear still pushing 30+ kt in the 3-6 km layer could
certainly make for organized elevated storms farther north.
There`s quite a lot of spread still in the position of the front
during the PM hours with models varying from far southern WI,
which would put our entire CWA in the all hazards warm sector,
or down into central IL which would pull most of the area out of
the stronger, surface-based severe threat, including the
tornado threat. More recent model runs have begun trending
toward a farther south solution, but it`d be unwise to get too
comfortable with that idea right now, especially when dealing
with such a rapidly-evolving system. All eyes over the next
couple of days will be on model trends regarding the placement
of that front.

The strong southerly mass response ahead of the system will
advect rich, deep moisture into the region with PWATs exceeding
1.5" into Wednesday setting the stage for more torrential
downpours with these storms. Additionally, storms during the
morning may attempt to backbuild into the higher instability
working in from the west. Given that much of the area is likely
in for at least a couple of rounds of showers and storms and
with the high soil moisture from recent heavy rains, flooding is
another concern for Wednesday, and that goes for areas on
either side of the warm front. Most recent runs of every piece
of available deterministic guidance that looks through
Wednesday evening resolves a widespread swath of over an inch of
QPF around the CWA with many suggesting 2-3"+ is possible over
a rather large area. WPC has placed us in a Slight Risk (Level 2
of 4) for excessive rain on Wednesday.

Outside of thunderstorms on Wednesday, anticipated gusty south
winds, especially across areas south of the front that can mix
into some stronger flow aloft. Additionally, afternoon
temperatures may vary sharply on either side of the warm front,
but there`s quite a lot of spread in how models handle temps on
Wednesday.

For the latter half of the week, that Hudson Bay upper low will
gradually get sheared out across the eastern half of Canada and
lock the Midwest into northwest upper flow pattern through the
weekend. Surface high pressure will work in from the west behind
Wednesday`s storm system and dry conditions are forecast for
Thursday and Friday. The high looks to move into our southeast
late Friday and introduce some mild return flow. Scattered
shower and thunderstorm chances then return as early as Saturday
with medium-range deterministic and ensemble guidance favoring
the late Sunday into Monday window for another organized system
of precip. Cooler than normal conditions late in the week look
to trend warmer for next week.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1225 PM CDT Mon Jun 15 2026

Main Concern:

- Potential for SHRA/TS Tuesday morning through early afternoon

Quiet VFR conditions will prevail through most of tonight.
Widely scattered SHRA may develop prior to sunrise over parts of
northern Illinois. As a cold front approaches during the
morning, SHRA coverage is expected to increase, along with the
potential for isolated to widely scattered TS. A few additional
TS may develop immediately ahead of the front in the early
afternoon, with higher TS coverage favored east of Chicago at
this time. Broadened out PROB30 TS mention for the Chicago
metro terminals with this issuance to capture the mid to late
morning and early afternoon windows. The cold front passage
between about 18-20z Tuesday will bring the TS threat to an end.

Breezy westerly winds gusting to near/around 20 kt this
afternoon will quickly diminish and become southwest with sunset
this evening. Southwest winds will gust to around 25 kt or so
ahead of the front through midday Tuesday, followed by a wind
shift to westerly with gusts to 25-30 kt.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 9 AM to 9 PM CDT Tuesday for the IL
     and IN nearshore waters.

&&

$$

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